Field of the Invention
The present invention relates to a conductive polymer composite and a substrate having a conductive film formed thereon with the conductive polymer composite.
Description of the Related Art
A polymer having a conjugated double bond (i.e. π-conjugated polymer) does not show an conductivity by itself; however, if an appropriate anionic molecule is doped therein, it can express an conductivity thereby giving a conductive polymer material (i.e. conductive polymer composition). As to the π-conjugated polymer, (hetero) aromatic polymers such as polythiophene, polyselenophene, polytellurophene, polypyrrole, and polyaniline, and a mixture thereof are used; and as to the anionic molecule (dopant), an anion of a sulfonic acid type is most commonly use. This is because a sulfonic acid, which is a strong acid, can interact with these π-conjugated polymers efficiently.
As to the anionic dopant of the sulfonic acid type, sulfonic acid polymers such as polyvinyl sulfonic acid and polystyrene sulfonic acid (PSS) are widely used (Patent Document 1). The sulfonic acid polymer includes a vinyl perfluoroalkyl ether sulfonic acid represented by Nafion (registered trademark); and this is used for a fuel cell.
Polystyrene sulfonic acid (PSS), which is a homopolymer of a sulfonic acid, has a sulfonic acid in the polymer main chain successively as the monomer unit thereof, so that this has a high doping effect to the π-conjugated polymer; and in addition, water dispersibility of the π-conjugated polymer after being doped can be enhanced. This is because the hydrophilicity is kept due to the excessively present sulfo group in PSS, whereby the dispersibility into water can be enhanced dramatically.
The polythiophene having PSS as a dopant shows high conductivity and can be handled as an aqueous dispersion, so that this is expected as a material for a coating-type conductive film in place of ITO (indium-tin oxide). As mentioned above, PSS is a water-soluble resin, and thus, it is hardly soluble in an organic solvent. Accordingly, the polythiophene having PSS as a dopant has a high hydrophilicity, but it is low in affinity with an organic solvent and an organic substrate, so that it is difficult to disperse it into an organic solvent or to form a film onto an organic substrate.
Besides, for example, when the polythiophene having PSS as a dopant is used in a conductive film for an organic EL lighting, the above-mentioned polythiophene having PSS as a dopant has an extremely high hydrophilicity; and therefore, a large quantity of water tends to readily remain in the conductive film, and in addition, the conductive film thus formed tends to readily absorb humidity from an outside atmosphere. As a result of them, there are problems that the light emitting capability of the luminous body of the organic EL is deteriorated due to chemical change thereof and that water agglomerates to give a defect as the passage of time thereby leading to shortening of the useful life of the entirety of the organic EL device.
In addition, since the polythiophene having PSS as a dopant has an absorption in the visible light region, in the case that this material is used as a film coated onto a transparent substrate such as a transparent electrode, there is another problem that the transmittance of the film is affected if the conductivity need for the function of the device is made up by the solid concentration or by the film thickness.
In Patent Document 2, conductive polymer compositions are proposed which are formed by a π-conjugated polymer formed of a repeating unit selected from thiophene, pyrrole, aniline, and a polycyclic aromatic compound, and a conductive polymer including a fluorinated acid polymer which can be wetted by an organic solvent; and it is shown therein that an aqueous dispersion of the conductive polymer can be obtained by combining, in an arbitrary order, water, a precursor monomer of the π-conjugated polymer, the fluorinated acid polymer, and an oxidant.
However, in the above-mentioned conventional conductive polymers, particles are agglomerated in the dispersion immediately after the synthesis thereof; and in addition, if an organic solvent is added therein to make it a highly conductive material as the coating material, agglomeration thereof is further facilitated so that the filterability thereof deteriorates furthermore. If the coating material is coated by spin coating without filtration, a flat film cannot be obtained due to the effect of the particle agglomeration; and as a result of it, there is a problem that this causes poor coating.